The invention relates to a method for the manufacture of a welded rotor of a fluid-flow machine.
A welded rotor of the generic type for a fluid-flow machine, for example for a gas-turbine plant, is described in European publication EP 0 844 367 A1. For cooling purposes, the rotor has hollow passages 5, 5a, 5b, etc., which extend around the rotor axis between two rotor disks welded to one another. With regard to the technical necessity of the hollow passages encircling the rotor axis, reference may be made to the abovementioned European publication, to which in addition reference is made with regard to all the details which are not described in full and which are required for the technical understanding of the cooling system on which the welded rotor is based.
In each case a specially designed insert ring 20, which at least partly defines each hollow passage on one side and is firmly welded to the rotor disks via appropriate welds, is provided for the peripheral sealing of the hollow passages 5, 5a, 5b, which for cooling purposes encircle the rotor described above (in this respect see FIG. 1 of the abovementioned European publication).
The geometrical design of the hollow space as well as the form of the insert rings are selected in such a way that work may be carried out with conventional welding techniques in order to produce the welds. Although this meets the desire for manufacturing techniques and conditions which are as simple as possible in the production and manufacture of welded rotors, the manufacture of the insert rings specially adapted to the geometry of the hollow passages requires high precision and high accuracy of alignment during assembly, as a result of which the manufacturing costs are in turn considerable. In addition, the insert rings each have a distance web, which projects into the interior of the hollow passage and impairs the free spreading of the cooling medium inside the hollow passage. These measures have been selected for reasons of simplified assembly with the use of conventional welding techniques. However, wake spaces, in which the cooling medium may collect or be trapped, inevitably form, as a result of which material damage cannot be ruled out.
Accordingly, one object of the invention is to develop a novel method for the manufacture of a welded rotor of a fluid-flow machine in such a way that, on the one hand, the individual components which are required for the assembly of the rotor are as simple and as cost-effective to produce as possible and are easy to join inside the rotor to be welded on the other hand. In particular, according to the present invention it is possible to fully utilize the advantages which are obtained, for example, by means of electron-beam welding. The manufacturing method is to work reliably with a higher process speed than is the case with the hitherto known methods for the manufacture of welded rotors of the generic type.
The method according to the invention for the manufacture of a welded rotor of a fluid-flow machine, through which rotor a cooling medium flows through inflow and outflow passages inside the rotor and which is composed of a plurality of rotor disks, which are connected to one another by welds running radially or largely radially relative to the rotor axis and in each case enclose with one another a hollow space, which runs around the rotor axis and interrupts the welds in such a way that a weld facing the rotor is directly adjacent to the hollow space, is developed by the following steps:
Two rotor disks directly adjacent to one another are firmly joined to one another along their mutual contact surfaces, preferably along a weld, for example with the use of conventional welding techniques. Like the abovementioned case of a welded rotor according to the teaching from European publication EP 0 844 367 A1, the two adjacent rotor disks, in the joined-together state, enclose a hollow passage, whose peripheral outside remote from the rotor axis is designed to be at least partly open. In addition, the rotor disks are designed in such a way that the enclose a gap, which directly adjoins the hollow space on the side facing away from the rotor and into which a ring element comprising at least two components is inserted. Both ring parts are then firmly joined to one another at their abutting surfaces inside the gap by means of electron-beam welding. Likewise, the side flanks of the components of the ring element which are fitted into the gap are firmly joined to the respective rotor disks by means of electron-beam welding.
By means of the method according to the invention, it is possible, with the use of the electron-beam welding technique and in virtually a single process step, to radially seal off to the outside the hollow passage, encircling the axis of rotation, between two rotor disks to be welded. To this end, a preferably two-piece ring is placed from outside into the open gap of the two rotor disks to be welded, the abutting surfaces of the ring parts being subsequently welded to one another by means of an electron beam. The side flanks of the ring elements are likewise welded to the corresponding rotor disks. This is possible with the use of electron-beam welding, since a welding process acting in the depth of the material is ensured by means of this technique.
In order to optimize the welding operation itself, centering lips, within which the welding beam is guided, are provided at the points to be welded.
Unlike the method described above, a further alternative method according to the invention for the manufacture of a welded rotor, of the generic category, of a fluid-flow machine provides for no splitting of the ring element, but rather uses a one-piece ring for closing off the hollow space at its peripheral outside. In addition, the method described below offers the possibility of also carrying out the joining operation with conventional welding techniques, for example by means of inert-gas, induction, ultrasonic or arc welding, just to mention a few alternative welding techniques.
To this end, a one-piece ring is inserted between two rotor disks to be welded before the two rotor disks are firmly welded to one another. In this case, one rotor disks provides a fixed stop surface, against which the one-piece ring, with one of its two opposite side flanks, abuts in a flush-fitting manner. The other rotor disks, on the other hand, is designed in such a way that the one-piece ring can be pushed at least a short distance over the other rotor disk. Here, the other rotor disks, adjacent to the hollow passage, which is formed by the joining of the two rotor disks, has an outside diameter which is smaller than the inside diameter of the one-piece ring.
The two rotor disks to be joined to one another are welded along at least one weld, which extends in the direction of the rotor axis starting from the hollow passage, which is enclosed by both rotor disks. During this welding operation, the one-piece ring is displaced in the direction of the rotor disk which, in the region of the hollow passage, has the outside diameter, described above, which is somewhat smaller than the inside diameter of the ring.
In this way, welding which is accessible from outside is possible at the weld point between the one and the other rotor disks, especially as the welding operation takes place through the hollow passage, which is open at the top.
For this operation, it is of advantage if the ring is fixed in its position described above by local sport welding. Other measures may of course also be taken in order to hold the ring in a position remote from the hollow passage during the welding.
Furthermore, the ring is released from its spot-welding point and pressed with its two side flanks against the fixed stop surface of the rotor disks. The welding operation to be carried out subsequently may be effected in the same way as in the case described above by means of electron-beam welding; conventional welding techniques may of course also be used.
In the state in which the ring bears against the stop surface of the rotor disks, this ring is welded to the rotor disks. If conventional welding techniques are used, first of all the bottom region between the fixed stop surface and the ring, the so-called root region, is welded. In this way, sufficient fixing of the ring to the stop surface of one rotor disks is ensured. The ring is subsequently partly or completely welded to the other rotor disk, so that the hollow passage open on one side is completely closed by the ring and the subsequent welding operations. Finally, the remaining intermediate gap between the fixed stop surface of one rotor disks is filled with the ring.
The manufacturing methods according to the invention and described above relate to a simplified assembly of welded rotors which provide cooling passages inside the rotor shaft for cooling purposes, cooling steam being driven through these cooling passages. Of decisive advantage is the utilization of the advantages associated with the electron-beam welding technique.